Read other letters about this article
Two thoughts/suggestions:
Tell the guy: "That's how it is. You'll have to figure out a way to deal with it, or move on, but there's nothing to discuss". If he resists this ultimatum, you'll know that he probably is the control freak that the other writers have described. If he wants you to be tested, fine, but other than that it's none of his business.
When a man (or woman) asks that question, smile sweetly, and say "Since (day you started dating), only one".